Based on datasheet -page 17:
GPIO registers are located on the ARM Cortex M0+ IO bus for fastest possible
single-cycle I/O timing, allowing GPIO toggling with rates of up to 15 MHz.
And I used a tiny code (based on the LPCOPEN library )to test it's speed:
Chip_GPIO_SetPinDIROutput(LPC_GPIO_PORT, 0, 12);
Chip_GPIO_SetPinState(LPC_GPIO_PORT, 0, 12, true);
Chip_GPIO_SetPinState(LPC_GPIO_PORT, 0, 12, false);
When I trace this GPIO pin by logic analyzer,It's toggling around 250 KHZ which is far away from mentioned value in datasheet.
I also used PLL to increase main clock and system clock for achieving better speed:
but even for different values 250KHZ is the most frequency which I cant overtake.Decreasing PLL speed cause decrements on output frequency of GPIO and also I know I can achieve better speed with assembly code but 250KHZ is so far away from datasheet & It seems MCU are not able to overtake from this limit(there ara same substance for 60MHZ/30MHZ - 60MHZ/15MHZ and so) Also 250KHZ is maximum speed which pins in the SPI peripheral state can toggled.